Due to their portability, connectivity, flexibility, and capabilities like that of a desktop computer, many people use laptops frequently and, indeed, daily. The keyboards of typical laptop computers and mobile devices (such as a smartphone) are thin, lightweight, and compact.
Unfortunately, conventional backlighting of keyboards adds complications, such as additional thickness to the overall keyboard assembly.
FIG. 1 shows an exploded view of a typical keyboard assembly 100 of a laptop computer or other mobile computing device. Such assemblies are also called keyboard stacks. The major components of this assembly 100 are shown without much detail. The primary purpose of FIG. 1 is to show the relationship amongst the major components of a typical keyboard assembly 100 of a laptop computer or mobile device.
Referring to FIGS. 1 and 2, the keyboard assembly 100 includes the following major component layers (from top to bottom): Key layer 102, keyboard mechanics layer 104, a sensor layer 106, a backplate layer 108, and a lightplate layer 110.
The key layer 102 includes, for example, a top bezel around one or more keytops 210. Below the key layer 102 is the keyboard mechanics layer 104. Typically, this layer 104 includes keypress functional components such as a resist-and-return structure 220 and a leveling structure 230. Often, the resist-and-return structure 220 components include a collapsible elastomeric plunger (i.e., “rubber dome”). Similarly, the leveling structure 230 often comprises a scissor mechanism 232, 244, or the like. The keyboard mechanics are discussed more below with regard to FIG. 2.
Under the keyboard mechanics layer 104 is the sensor layer 106. The purpose of the sensor layer 106 is to detect a keypress of one or more of the keys 200. To that end, it has electronic circuitry (e.g., one or more sensors 260) to sense the downward pressing of the key 200 by a user. The most common type of sensor 260 utilizes a conductive or contact switch under each key. Other sensing technologies (such as capacitive and electrical resistance) may also be employed. The sensor layer 106 is also often called the “keyswitch” layer or the “sensor membrane” layer.
A conventional keyboard assembly 100 typically utilizes a sensor membrane layer 106 of at least three substrates and one or more conductive-based switches 260 to detect key depressions. A first substrate and second substrate each have contact switch circuitry. The first and second substrates are separated by a third non-conductive substrate disposed therebetween. The non-conductive substrate between the two conductive substrates has a hole therethrough that allows the underkey contacts of each conductive substrate to trampoline together upon a keypress. This action closes a switch 260 and indicates a keypress.
A controller (not shown) associated with the keyboard assembly 100 detects that a particular key 200 is depressed and sends that information to a processor or other computing device. Of course, other keyboard assemblies 100 can use different key press detection technologies, such as capacitive and resistive.
The keyboard mechanics 230 are attached to the rigid backplate 240 of the backplate layer 108. Typically, such a backplate 240 (i.e., “backer”) is made from a strong material like steel, aluminum, or other metal. Under the backplate layer 108 is the lightplate layer 110.
The lightplate 270 (i.e., light guide plate or lightguide) of the lightplate layer 110 can employ conventional light-emitting diodes (LEDs) as an illuminant. Typically, the LEDs are mounted on the outer edge of the keyboard assembly 100 and away from the keys 200 themselves. The light from the LEDs is guided to the interior of the keyboard 100 via the light guide plate 270. Diffusers (e.g., etched dots or patterns) under the keys catch the light and diffuse it under each key. Therefore, in an area with weak or no light, the legends on the keys 200 of the keyboard 100 can be seen by the light emitted from the light guide plate 270, thereby facilitating to operate.
Generally, a conventional lightplate layer 110 has a light-generating component (e.g., LEDs) to one or more edges of the keyboard 100 so as that it is not under any actual keys 200. That light-generating component is thick, because it generally comprises a flexible printed circuit (FPC) that contains conventional LEDs.
The conventional lightplate layer 110 is designed to diffuse the light of its light guides through diffusers. A diffuser may be a series of unevenly-spaced bumps, etched dots, or some uneven pattern to scatter the light of the light guide 270. The density of bumps increases further away from the light source according to a diffusion equation. The diffused light then travels to either side of the diffuser. The front of the lightplate 270 faces the actual desired goal, which is the underside of the key. The back of the lightplate 270 has a reflector to reflect otherwise wasted light back toward the underside of the keytop 210.
The conventional lightplate layer 110 has three substrates (from top to bottom): a Mylar mask substrate, a light guide substrate, and reflector substrate. The Mylar mask substrate masks the key webs. The light guide substrate is a clear material (e.g., silicon) consisting of light guides (e.g., light paths) and diffusers under keys to diffuse the light on the guides. The reflector substrate reflects the light up towards the keys above. The reflector substrate is sometimes made of aluminum foil, sometimes merely a white-pigmented surface or, as in the 3M Vikuiti ESR, consists of hundreds of polymer layers of alternating low and high refractive index. A conventional lightplate layer 110 is about 0.25-0.5 mm thick.
FIG. 2 illustrates a side elevation view of a simplified key assembly (“key”) 200 of a conventional keyboard 100 of a typical computer system. The components of the key assembly 200 are not shown to scale. Also, they are not shown with proper relative proportions to the size and thickness of the other components. Rather, the components are shown in the order of the keyboard stack described and with regard to the relationships to each other.
Stripped down to its essentials, the conventional key assembly 200 includes a keycap 210 (e.g., keytop), a collapsible elastomeric plunger (i.e., “rubber dome”) 220, a scissor-mechanism 230, a rigid base 240, a keyswitch sensor 260, and a lightplate 270.
The layers of keyboard assembly 100 correspond to this key assembly 200 in the following manner:                the key layer 102 includes the keycap 210 (typical thickness is 0.3-0.5 mm);        the key mechanics layer 104 includes the rubber dome 220 and scissor-mechanism 230 (typical thickness is 1.5-2.5 mm);        the sensor layer 106 includes the keyswitch sensor 260 (typical thickness is 0.25 mm);        the backplate layer 108 includes the base 240 (typical thickness is 0.25-0.5 mm);        the lightplate layer 110 includes the lightplate 270 (typical thickness is 0.25-0.5 mm).        
The rubber dome 220 provides a familiar snap-over feel to a user while she presses the key 200 to engage the keyswitch sensor 260 under the keytop 210. The primary purpose for the scissor-mechanism 230 is to level the keytop 210 during its keypress.
Typically, the scissor mechanism 230 includes at least a pair of interlocking rigid (e.g., plastic or metal) blades (232, 234) that connect the keycap 210 to the base 240 and/or body of the keyboard 100. The interlocking blades 232, 234 move in a “scissor”-like fashion when the keycap 210 travels along its vertical path, as indicated by Z-direction arrow 250. The arrangement of the scissor mechanism 230 reduces the wobbling, shaking, or tilting of the keycap 210 while the user is depressing it.
As can be seen in both assemblies (100 and 200), the light from the lightplate 270 (e.g., lightplate layer 110) must make its way past many obstructions to arrive under the keycap 210 and to ultimately illuminate a transparent or translucent legend (e.g., “A” or “Shift”) of a key 210. The obstructions include the backplate layer 108, sensor layer 106, keyboard mechanics layer 104 (such as rubber dome 220 and scissor-mechanism 230), and other structures under the keycap 210 itself.
In conventional keyboards 100, a narrow unobstructed path is designed under each key 210 to aid the under illumination of each key 200. Holes are punched in the backplate 240. Clear windows are strategically placed in the sensor layer 106. Of course, the diffusion etchings in the lightplate 270 are placed under those narrow paths under the keys 200.
Of course, these narrow unobstructed paths affect the design and function of the other components of the keyboard stack 100. Too many holes compromise the rigidity of the backplate layer 108. Arrangement of the keyboard mechanics 220, 230 cannot be adjusted too much without compromising its functionality and durability.
One apparent option to reduce obstruction is to place the lightplate layer 110 higher in the stack 100, for example, above the backplate layer 108 or above the sensor layer 106. However, using conventional materials, this cannot be accomplished.
While not shown, the keyboard assemblies 100 include vertical support structures. To provide structural support to the whole keyboard 100, the vertical support structures attach to the backplate layer 108. The backplate layer 108, in turn, is attached to the housing of the device itself.
Because of the vertical support structures, the lightplate layer 110 is traditionally placed below the backplate layer 108 rather than above it. When it is below the backplate layer 108, the lightplate layer 110 can be free of holes or, at least, have a minimum of holes therethrough. Above the backplate layer 108, the lightplate layer 110 must have several holes through which the vertical supports would pass therethrough.
In short, functionality of a conventional lightplate 270 is compromised greatly by having holes. The holes would cut or significantly redirect the light guides in the lightplate 270. Additional holes requires more redirection of light guides and limits the real estate available on the plate 270 for such guides. Every bend in the light guide leaks light.
Overall, this reduces the amount of light that ultimately arrives at each key 200. The keys 200 that are distant from the LEDs are most affected. Indeed, the number and placement of holes might result in little or no light arriving at the keys 200 that are particularly distant from the LEDs.
The background of U.S. Pat. No. 5,746,493 says this about conventional light guides and their issues:                A light guide or light conductor used to transmit light for illuminating a display and keyboard in a device typically is formed as a planar element of translucent material. A light guide is generally positioned as a layer on one side of the device's display panel and keyboard. Light sources, typically LEDs, are positioned along an edge of the light guide and light transmitted into it is diffused and distributed by the light guide to the display and keyboard.        A problem in conventional light guides is that light is not distributed uniformly, and the display panel and keys are accordingly not uniformly illuminated. Bright and dark areas thus result in the display and keys, which detracts from the appearance of the device.        This problem is related in part to the manner in which the light sources are positioned and/or coupled to the light guide. Conventionally, light sources are simply positioned along an edge of the light guide for the display panel and additional lights sources positioned in holes located in the interior of the light guide near the key holes. Light from the sources on the edge of the light guide is not uniformly transmitted across the edge of the light guide.        The problem is also related to how light exiting the light guides is handled at the edges. Light that strikes the edges is in part lost through the edge and in part reflected back in the light guide in a way that does not provide much useful illumination.        
The Detailed Description references the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same reference number references like features and components throughout the drawings.